Hunt RK et al. (1987), Cell patterning in pigment-chimeric eyes in Xen...

XB-ART-28158

Proc Natl Acad Sci U S A 1987 May 01;8410:3302-6.

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Cell patterning in pigment-chimeric eyes in Xenopus: germinal transplants and their contributions to growth of the pigmented retinal epithelium.

Hunt RK , Cohen JS , Mason BJ .

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We have examined the process by which small groups of pigmented germinal cells transplanted orthotopically from stage 30-38 donor embryos into stage 28-38 albino hosts contribute new postmitotic cells to the pigmented retinal epithelium of the growing larval eye in Xenopus. In the great majority of chimeric eyes, the transplant healed to occupy a small arc-territory at the intended dorsal or anterior position on the host germinal zone. Over the course of subsequent weeks, the transplanted germinal cells added new mitotically quiescent cells to the distal rim of the pigmented retinal epithelium and so gave rise to an elongating black sector on the growing larval eye. Cellular details at the boundaries of the graft-derived sector were stable over time; the accumulation of such landmarks provided a summary record--in the proximodistal axis of the older eye--of the growth history of the transplant. Case-to-case variation among both groups of transplants suggested a measure of indeterminancy in the details of germinal cell growth.

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Species referenced: Xenopus laevis
Genes referenced: adm notch1

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	FIG. 1. (a) Schematic of the GZ in larval Xenopus eye. The GZ is a bilayered ring, whose outer pigmented germinal cells (circles) form a smooth continuous layer with the PRE (squares) proximally and the iris (IR) distally, and whose inner neuroepithelial layer is continuous with neural retina. Animals sacrificed immediately following an injection of 3H-labeled thymidine at any larval stage from late-30 through metamorphosis show labeled cells only in the GZ proper. Animals sacrificed many weeks after a pulse of 3H-labeled thymidine show a "birthdate ring" (BR) of labeled cells displaced from the GZ by new growth, formed after the pulse, in which the label has been diluted to background. (b) Three-dimensional pattern of growth is annular with the GZ sitting on the rim of the retinal epithelia. Immediately surrounding the optic nerve are the oldest cells-the "back" of the eye that differentiated in the 2.5- to 4-day embryo. The rest of the eye can be viewed as the cumulative set of BRs; the earlier ones are at the back; and the more recent BRs are ever closer to the front-here visualized as PRE contours in a chimeric eye reconstructed from serial sections cut approximately perpendicular to the optic axis. (c) Operative schematics for the orthotopic transplantation of dorsal (12 or 1 o'clock) or anterior (3 o'clock) germinal cells between right eyes of embryos.
	FIG. 2. First and last photo of photorecord of case SI 2631, prepared by orthotopic transplantation of dorsal (1 o'clock) germinal cells from the right eye of a stage-34 pigmented (XBL hybrid) donor embryo into the right eye of a stage-34 albino host embryo; magnification xl. (a) In a lateral view of the transilluminated stage-40 embryo, the transplant had blackened and was seen with reference to the eye and head, including the opaque central circle that is the site for the yet undeveloped pupil and lens and to the ventral fissure (vf). (b-d) Three views, at the same magnification as in a, of the chimeric eye after 131 days of larval growth to stage-63/4. (b) In lateral view, pigmented cells on the front of the eye could be assigned to the iris (ir), whose projection on the eye surface occupies the halo territory immediately encircling the pupil (p); the GZ (gz), which occupies the halo domain just proximal to the ir on the rim of the PRE; and the PRE that extends smoothly from the gz round the back of the eye. (c) The dorsal view is dominated by the PRE (pre), but also shows the lens and cornea protruding laterally. The spatiotemporal axis of cell birthdates in the pre (as inferred from the data in Fig. 3) extends from the back of the eye round to the pre margin and more recently added cell groups are marked by smaller arrows. (d) An unobstructed medial view of the eye-photographed after enucleation, fixation, and removal of the lens and sclera-allowed the oldest transplant cells to be seen on the back of the eye, with reference to the optic nerve (on) and ventral fissure (vf).
	FIG. 3. (a) Further excerpts from the photorecord of case SI 2631; magnification x 19. Growth proceeds from top to bottom (arrows); for each photographic timepoint, the tadpole age [in days (d) postoperation] and developmental stage (17) are at the left. At each stage, two or more views of the eye are shown, and each is appropriately labeled as dorsal (D), lateral (L), dorsolateral (DL), etc. All three photomicrographs from the last timepoint (131 days, stage 63/4) were photographed in buffer after immersion fixation (as in Fig. 2d): in addition to providing an unobstructed medial view of the eye, the eye can be rotated on its axis to provide oblique views such as anterodorsal (AD) and anterodorsolateral (ADL) to optimally visualize the black sector in PRE (compare with Fig. 2c pattern taken just before eye removal). (b-f) Montages formed from x2.5 blow-ups ofthe D view and the DL or L view shown in a for the corresponding photographic timepoint. Boundary characters established since the previous photosession are bracketed by arrows on each montage. Note that new boundary characters are added to the distal rim ofthe PRE and form a cumulative proximodistal record of the transplant's growth. For reference, the pupil (P) is labeled, and the proximodistal axis of the sector runs from top down in each montage. GZ is labeled on the last montage.
	FIG. 4. (a) Excerpts from the photorecord of case SI 1918, prepared by transplantation of dorsal (1 o'clock) germinal cells from a stage-34 pigmented (4nXL) donor embryo into the right eye of a stage-33 albino host embryo; magnification x17. (b) Blow-up (x3) of the 1-day photomicrograph showing the transplant in relation to the pupil (P) and ventral fissure (VF); (c-e) montages prepared from x2.5 blow-ups of the pair of views shown in a for the corresponding timepoint, and demonstrating the appearance of boundary characters; views are labeled as in Fig. 3 with the additional abbreviation- DM, dorsomedial view. This case also illustrates the period of settling and stretching as new boundary characters acquired their permanent form. For example, the notch-like character emerging on the right black/white boundary from the GZ at stage 49 (d) expands in the circumferential direction and becomes slightly curved by stage 50/1 as the character is displaced from the GZ by more recent growth.
	FIG. 5. (a) Excerpts from the photorecord of case SI 719, prepared by transplantation of anterior (3 o'clock) germinal cells from the right eye of a stage-33 pigmented XB donor embryo into the right eye of a stage-35 albino host embryo; magnification x 17. (b) Blow-up (x3) of the healed transplant at 3 days postoperation, showing tissue that had become postmitotic before stage 44 and the relation of the transplant to the pupil (P) and ventral fissure (VF). (c-e) Montages from x2.5 (c) or x2 (d, e) blow-ups of the pair of views shown in a for the corresponding timepoint. The last montage (e) is prepared from only the dorsolateral (DL) and anteromedial (AM) views and labeled with the cumulative record of proximodistal cell birthdates. Note that the rotation of views is somewhat oblique, biased toward dorsal in views of the front of the eye at later stages; this choice of views is because germinal descendants of the transplant were gradually displaced from anterior to more dorsal positions over time, and therefore, the mature sector veers from anterior on the back of the eye toward dorsal on the front of the eye.

References [+] :

Beach, Patterns of cell proliferation in the retina of the clawed frog during development. 1979, Pubmed, Xenbase